Thanks for the explanation very intresting....How much does a tower brace increases rigidity in a car about 10-15%? Or more?

 

the rigidity of a car isn't just a number. theres various forms of it and its different in different spots.

a strut tower bracee specifically helps ensure that the strut towers down flex, thereby helping to ensure that suspension geometry remains as it should be under hard cornering forces.

but the z06 doesnt have 'strut towers' so you couldnt really put a brace on them.

 

Good answer! In automotive structures, engineers are concerned with both overall stiffness and localized stiffness where loads are high. Overall stiffness is usually expressed as a first mode resonant frequency, and it can be either bending or torsion. A higher number is better, and I recall the first mode for the C5 is 23 Hertz, bending. This is probably the highest in the industry for an open car and exceeds many fully enclosed cars.

As an example of localized stiffness concerns, the C5's shock mounts were beefed up and the jounce bumpers were redesigned from early prototypes based on GM's severe pothole test as indications from both computer simulations and actual testing showed that they needed to be reinforced.

As far as how much a strut tower brace helps stiffen a strut suspension car, I don't have any data, but, especially on performance oriented models, most OEMs install them at the factory, and a lot of aftermarket braces are sold, either to replace the factory braces or provide a brace where it was not original equipment.

Duke

 

So the Z06 must be a little higher than the Coupe 23 hertz.....

You can also notice the rigidity of a car when you are traveling on a bad rough road where cowl shake is most likely to be notice.

I think that the C5 structure was such a major improvement over the C4 that even today seven years later is still one of the best structures...

The perfect example is the C6 which basically is going to continue to use the C5 structure with minor changes....

I will like to know what are those minor changes?

 

Yes, the FRC is stiffer. I've never seen any data on how much, but I an feel the increased chassis stiffness on a bumpy/wavy road. The C4 was probably no more than about 15 Hertz, so the C5 was a major improvement, and I expect the C6 will be a little better, but not a quantum leap.

Duke

 

Actually from what i have been reading the Corvette structure should be stiffer than the Porsche 911 because the Porsche uses a Monocoque unibody chassis which is not ideal for a high performance sports car because is made from STAMPED steel. Stamped steel is not as strong as Hydroforming, forging or casting.

The only STAMPED part in the Corvette chassis is its Backbone...The rails we know are hydroformed, the Crossmembers are Cast aluminum, the Floor uses balsa wood with composite so is not STAMPED steel, the windshield frame is aluminim probably castings with extrusions. The bumper beams i am not sure but probably are also hydroformed.

In addition to that High Strenght Steel i think is used in all the Vette Structure where in the 911 High Strenght Steel is used in certain areas...

What do you think?

 

no telling.
id wager they are both 'stiff enough' and it isn't really an issue.

=)

 

Unibody cars can be very stiff. They are almost always stiffer than body-on-frame construction, and offer the advantage of much better packaging efficiency. The best modern unibody sedans have a first mode in the range of 25 Hertz, and the smaller the car, the stiffer it usually is. Porsche coupes have always been known for excellent structural rigidity. I recently had an opportunity to ride in/drive a friend's newly acquired '70 911S and was damned impressed with it.

I've never seen any structural stiffness data on modern Porsches, but I expect the closed coupes are at least as stiff as the C5, but the open models are probably not quite as good.

The biggest structural design issue in the industry has always been obtaining sufficient rigidity from an open design, and the C5 coupe is considered open, even with the top on. Achieving a 23 Hz first mode with an open car, which is in the range of the best closed cars, was quite an engineering feat, and by bonding the roof on the FRC, a very stiff chassis becomes even stiffer, and you can feel this SOTP if you drive a coupe and FRC back to back.

The C5 structure is unique in the entire auto industry. It is not "unibody" and it is not "body-on-frame". I call it a "hybrid backbone/siderail" structure and it's a superb piece of engineering.

Duke





[Modified by SWCDuke, 10:42 AM 7/10/2003]

 

Any news release that mentions the Nurburing laptime from GM??
Also, I've heard that there are two different lap lengths... one is full lap
another is called BTG (bridge to gate?.. or something like that)... anyone
know which one did the Z06 do?

Thanks,

 

What i read is that it did 7 min 56 seconds......Very few cars have done under 8 minutes in that demanding track.....

I just read an article i believe its was in the Corvette Magazine about the 04 Z06 new shocks and the guy that tested the car with the new shocks said that the difference in handling is very evident.....He tested it in a Michigan Track and the 04 model is faster obviously in the corners and the car than the 03...

You can exit the corners faster and with more confidence!!!!!He also said that there is no penalty in ride comfort great achivement....... :thumbs:

 

I was reading last night an article in which they were comparing the 04 Audi A8 Space Frame versus the new 04 Jaguar XJ aluminum Monocoque unibody and i learn a lot.

They say that the A8 chassis is a little lighter than the Jaguar 474 vs 485 lbs also that the Jaguar structure because uses more Stamped Pressing Sheets is less costly and is slightly less rigid...The A8 uses less stampings sheets and more die castings and extrusions parts so it has the edge in rigidity over the Jag...

Still the new XJ aluminum unibody is one heck of a chassis...Unlike the Audi it uses aeropace adhesives to join the Aluminum no welding is use....

 

Duke you'll like this quote from my friend that is one of the head engineers at Porsche, "Porsche, a bad design engineered to perfection". Struts, rear engine, tall green house.

 

Love it!

I also remember a quote from the late Porsche racer Bob Akin, who, back in the late seventies or early eighties on discussing the 935 said something to the effect: "The 935 is proof that you can't turn a pig into a racehorse, but you can make an awfully fast pig."

Back in this era the plan of Porsche chairman Peter Schutz was to phase out the 911 and continue to develop front engine/rear transaxle cars like the 924/944 and 928, including a four door sport sedan, but the Porsche faithful kept buying 911s even though the engineers long recognized its basic architectural deficiencies. The Porsche family finally got rid of Schutz and gave the 911 a new life. Schutz was technically correct, but politically out of step.

The front "mid engine" (engine set back so the front of the engine is at or behind the front axle centerline)/rear transaxle architecture is probably the optimum design for a street sports car when you consider passenger packaging, cargo volume, and stable handling, which is why we will probably never see a mid engine Corvette. If GM ever does build a mid engine car, I think they should call it something else. The front engine architecture is just too much a Corvette icon at this point, and it is fundamentally correct. Maybe Cadillac will built a production version of the Cien.

Duke


[Modified by SWCDuke, 5:29 PM 7/10/2003]

 

Yeah the 911 has come a long way we have to give Porsche credit for making this not ideal configuration to one of the best handling cars in the world. Is incredible how good the 911 handles when you consider that it has 60 percent of its weight in the rear...

I think that Porsche racehorse is going to be the Carrera GT no struts, midengine, low greenhouse and Carbon fiber structure......


[Modified by ivan111, 1:41 AM 7/11/2003]

 

Several months ago I watched a factory MULE Z running on a track in the West.Stock tires,stock wheels.LOOKED like stock suspension.It ran 1/2 second faster than the typical T1 car or VIPER on the same track,This car had just arrived from testing at the "Ring"in Germany.Mule was faster after the apex of each corner and on a high speed sweeper curve he held a line that my Z cannot do.Also testing where V8 Caddy,s--most impressive .

 

Improvement to the Z's shocks is ong overdue, as they (and all the other Sachs shocks) could certainly use A LOT of work. Rebound control in the rear, in particular, is horrible. That was also the case on my Z51 Coupe. Just changing to Bilsteins on that car vastly improved the high speed stability of the car. My (stock) '02 Z is better than the Coupe was when stock, but the rear floatiness at high speed is still there.

The Nordschliefe segment of the 'Ring will rapidly expose any weakness in high-speed stability, and I would bet the Z06 testers got a real eye-opener.

In my humble opinion, the Corvette team should just have used the Bilstein monotube shock on the Z51 and Z06 suspensions from the getgo. It is simply a better design. Chevy has gone that route before on the C4.

FWIW, the Z06 is considered to be 11% stiffer (torsional) than the closed coupe...I think the freq. is 25.6Hz, but that's based on memory so may be incorrect.

 

Is incredible how a simple shock change can enhance the handling of an already a great handling car....

I can't wait to see what enhancements are they going to do to improve the C6 handling..

Will the C6 coupe outhandle the C5 Coupe?

I think so but what we don't know if what chassis improvements are going to allow that!!!!!

 

Intresting facts about the Z06 rigidity, where did you see that?